Add pcqm4m multi-gpu example: large scale graph regression

[Kh4L]

This PR adds OGB LSC example pcqm4m https://ogb.stanford.edu/docs/lsc/pcqm4mv2/ , large scale graph regression: predicting the HOMO-LUMO energy gap in electronvolt (eV) given 2D molecular graphs.

Most of the code is adapted from the https://github.com/snap-stanford/ogb repository.

[puririshi98]

@akihironitta let us know if anything else needed to get this merged?